1. Field of the Invention
The present invention relates to an image processing system, more particularly to an image processing system wherein a storage section is accessed directly by an external controller in an image processing mode in which to execute image processing.
2. Description of the Related Art
An image forming apparatus, such as a digital color copying machine, is provided with an image processing section configured to process images read from a scanner. An example of the image processing section is an application specific integrated circuit (ASIC). The ASIC incorporates a RAM to temporarily store data required for image processing. Normally, the RAM operates based on equal clocks as an image-processing logic section provided inside the ASIC. The clocks on which to operate the image-processing logic section may vary in frequency in accordance with an image processing mode selected. For example, the frequency of the clocks in a color image processing mode may be half that of the clocks used in a monochrome image processing mode because of the sensitivity difference between CCDs. As can be seen from this, when the clocks based on which to operate the components of the ASIC change, the frequency of the clocks supplied to the RAM changes accordingly. That is, in the case of an image processing mode in which the clocks are slow in terms of the operation of the RAM, the RAM operates in synchronism with those clocks. If the RAM is directly accessed by an external controller of the ASIC in the image processing mode, the clocks based on which to operate the RAM are slowed in accordance with that image processing mode. Therefore, the controller requires a long access time, and the efficiency of the entire system including the ASIC is inevitably low.